Just Cc-ing some Linux, block, and Xen on CentOS people...

On Mon, 2016-06-06 at 11:24 +0300, Evgenii Shatokhin wrote:
> (Resending this bug report because the message I sent last week did
> not 
> make it to the mailing list somehow.)
> 
> Hi,
> 
> One of our users gets kernel panics from time to time when he tries
> to 
> use his Amazon EC2 instance with CentOS7 x64 in it [1]. Kernel panic 
> happens within minutes from the moment the instance starts. The
> problem 
> does not show up every time, however.
> 
> The user first observed the problem with a custom kernel, but it was 
> found later that the stock kernel 3.10.0-327.18.2.el7.x86_64 from 
> CentOS7 was affected as well.
> 
> The part of the system log he was able to retrieve is attached. Here
> is 
> the bug info, for convenience:
> 
> ------------------------------------
> [    2.246912] kernel BUG at drivers/block/xen-blkfront.c:1711!
> [    2.246912] invalid opcode: 0000 [#1] SMP
> [    2.246912] Modules linked in: ata_generic pata_acpi
> crct10dif_pclmul 
> crct10dif_common crc32_pclmul crc32c_intel ghash_clmulni_intel 
> xen_netfront xen_blkfront(+) aesni_intel lrw ata_piix gf128mul 
> glue_helper ablk_helper cryptd libata serio_raw floppy sunrpc
> dm_mirror 
> dm_region_hash dm_log dm_mod scsi_transport_iscsi
> [    2.246912] CPU: 1 PID: 50 Comm: xenwatch Not tainted 
> 3.10.0-327.18.2.el7.x86_64 #1
> [    2.246912] Hardware name: Xen HVM domU, BIOS 4.2.amazon
> 12/07/2015
> [    2.246912] task: ffff8800e9fcb980 ti: ffff8800e98bc000 task.ti: 
> ffff8800e98bc000
> [    2.246912] RIP: 0010:[<ffffffffa015584f>]  [<ffffffffa015584f>] 
> blkfront_setup_indirect+0x41f/0x430 [xen_blkfront]
> [    2.246912] RSP: 0018:ffff8800e98bfcd0  EFLAGS: 00010283
> [    2.246912] RAX: ffff8800353e15c0 RBX: ffff8800e98c52c8 RCX: 
> 0000000000000020
> [    2.246912] RDX: ffff8800353e15b0 RSI: ffff8800e98c52b8 RDI: 
> ffff8800353e15d0
> [    2.246912] RBP: ffff8800e98bfd20 R08: ffff8800353e15b0 R09: 
> ffff8800eb403c00
> [    2.246912] R10: ffffffffa0155532 R11: ffffffffffffffe8 R12: 
> ffff8800e98c4000
> [    2.246912] R13: ffff8800e98c52b8 R14: 0000000000000020 R15: 
> ffff8800353e15c0
> [    2.246912] FS:  0000000000000000(0000) GS:ffff8800efc20000(0000) 
> knlGS:0000000000000000
> [    2.246912] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    2.246912] CR2: 00007f1b615ef000 CR3: 00000000e2b44000 CR4: 
> 00000000001406e0
> [    2.246912] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
> 0000000000000000
> [    2.246912] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 
> 0000000000000400
> [    2.246912] Stack:
> [    2.246912]  0000000000000020 0000000000000001 00000020a0157217 
> 00000100e98bfdbc
> [    2.246912]  0000000027efa3ef ffff8800e98bfdbc ffff8800e98ce000 
> ffff8800e98c4000
> [    2.246912]  ffff8800e98ce040 0000000000000001 ffff8800e98bfe08 
> ffffffffa0155d4c
> [    2.246912] Call Trace:
> [    2.246912]  [<ffffffffa0155d4c>] blkback_changed+0x4ec/0xfc8 
> [xen_blkfront]
> [    2.246912]  [<ffffffff813a6fd0>] ? xenbus_gather+0x170/0x190
> [    2.246912]  [<ffffffff816322f5>] ? __slab_free+0x10e/0x277
> [    2.246912]  [<ffffffff813a805d>]
> xenbus_otherend_changed+0xad/0x110
> [    2.246912]  [<ffffffff813a7257>] ? xenwatch_thread+0x77/0x180
> [    2.246912]  [<ffffffff813a9ba3>] backend_changed+0x13/0x20
> [    2.246912]  [<ffffffff813a7246>] xenwatch_thread+0x66/0x180
> [    2.246912]  [<ffffffff810a6ae0>] ? wake_up_atomic_t+0x30/0x30
> [    2.246912]  [<ffffffff813a71e0>] ?
> unregister_xenbus_watch+0x1f0/0x1f0
> [    2.246912]  [<ffffffff810a5aef>] kthread+0xcf/0xe0
> [    2.246912]  [<ffffffff810a5a20>] ?
> kthread_create_on_node+0x140/0x140
> [    2.246912]  [<ffffffff81646118>] ret_from_fork+0x58/0x90
> [    2.246912]  [<ffffffff810a5a20>] ?
> kthread_create_on_node+0x140/0x140
> [    2.246912] Code: e1 48 85 c0 75 ce 49 8d 84 24 40 01 00 00 48 89
> 45 
> b8 e9 91 fd ff ff 4c 89 ff e8 8d ae 06 e1 e9 f2 fc ff ff 31 c0 e9 2e
> fe 
> ff ff <0f> 0b e8 9a 57 f2 e0 0f 0b 0f 1f 84 00 00 00 00 00 0f 1f 44
> 00
> [    2.246912] RIP  [<ffffffffa015584f>] 
> blkfront_setup_indirect+0x41f/0x430 [xen_blkfront]
> [    2.246912]  RSP <ffff8800e98bfcd0>
> [    2.491574] ---[ end trace 8a9b992812627c71 ]---
> [    2.495618] Kernel panic - not syncing: Fatal exception
> ------------------------------------
> 
> Xen version 4.2.
> 
> EC2 instance type: c3.large with EBS magnetic storage, if that
> matters.
> 
> Here is the code where the BUG_ON triggers (drivers/block/xen-
> blkfront.c):
> ------------------------------------
> if (!info->feature_persistent && info->max_indirect_segments) {
>      /*
>          * We are using indirect descriptors but not persistent
>          * grants, we need to allocate a set of pages that can be
>          * used for mapping indirect grefs
>          */
>      int num = INDIRECT_GREFS(segs) * BLK_RING_SIZE;
> 
>      BUG_ON(!list_empty(&info->indirect_pages)); // << This one hits.
>      for (i = 0; i < num; i++) {
>          struct page *indirect_page = alloc_page(GFP_NOIO);
>          if (!indirect_page)
>              goto out_of_memory;
>          list_add(&indirect_page->lru, &info->indirect_pages);
>      }
> }
> ------------------------------------
> 
> As we checked, 'info->indirect_pages' list indeed contained around
> 30 
> elements at that point.
> 
> Any ideas what may cause this and how to fix it?
> 
> If any other data are needed, please let me know.
> 
> Regards,
> Evgenii
> 
> References:
> [1] https://bugs.openvz.org/browse/OVZ-6718
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)